FIELD OF THE INVENTION
The invention relates to a device for ensuring, for an unlimited period of time, the thermal protection of a structure liable to be located in an environment which may be subject to virtually unlimited temperature rises.
Such a thermal protection device has numerous applications with respect to the protection of human beings and equipment both on the ground and in the atmosphere. However, the invention is of particular interest for those applications involving ambient pressure variations and the application to the structure to be protected of variable accelerations and decelerations.
The invention more particularly relates to a thermal protection device incorporating a retention layer initially impregnated with a fluid substance in the liquid state when the external temperature does not exceed a certain threshold. Such a thermal protection device is normally referred to as a "transpiring" thermal protection. Thus, when subject to an external thermal action, the fluid substance initially in the liquid state and normally retained in the retention layer progressively vaporizes in the atmosphere from the retention layer. The thus formed vapour is reheated by the external thermal flux before escaping into the atmosphere, so that the heat quantity removed is higher the higher the thermal flux to which the device is exposed. Therefore the liquid-impregnated retention layer is sometimes referred to as a "vaporizer-superheater element" or "hydrator - superheater element". The configuration of such a "transpiring" thermal protection and its operating procedure are described in detail in FR-A-2 512 169.
As is also described in the latter document, such a "transpiring" thermal protection can be equipped with a system making it possible to reinject fluid substance in the liquid state into the retention layer, so as to permit an increase in the life of the thermal protection beyond the time necessary for the complete vaporization of the fluid substance in the liquid state initially contained in the retention layer.
It is generally possible without any particular difficulty to reinject with the aid of the pump fluid substance in the liquid state into the retention layer of a "transpiring" thermal protection under substantially constant pressure and acceleration conditions, such as occurs with most terrestrial applications of such a thermal protection. However, the reinjection of the fluid substance in the liquid state into the retention layer becomes very complex when the envisaged application assumes significant pressure and acceleration variations, as is particularly the case for aeronautical and space applications. It then becomes virtually impossible to supply the retention layer in a homogeneous manner, so that the thermal protection becomes locally ineffective in certain zones. Therefore for such special applications no thermal protection exists which is able to fulfil its function for an unlimited period, so that it can be used again, if necessary, without any special maintenance.
The present invention specifically relates to a thermal protection device of the "transpiring" thermal protection type, whose original design makes it possible to ensure a homogeneous resupply of fluid substance to the retention layer of the thermal protection, no matter what the pressure and acceleration variations which are undergone by the structure carrying said thermal protection.
The invention also relates to a thermal protection device of the "transpiring" thermal protection type, whose original design makes it possible to protect a structure liable to be subject to significant pressure and acceleration variations for an unlimited period, no matter what the ambient temperature, and such that the thermal protection device can be reused for an undetermined number of missions without requiring replacement.